The primary aim of this trial is to characterize the pharmacokinetics of a single oral dose of 2.5 or 5.0 mg ridogreal in pediatric patients age >8 to <18 with U.C. The secondary aim is to evaluate the safety and the tolerability (adverse experiences) of oral ridogrel 2.5 mg given to pediatric patients with ulcerative colitis. In December 1998 the Mallinckrodt General Clinical Research Center was notified by the principal investigator that the sponsor, Pharmaceutical Research Associates, Inc., had been notified by Jansen Research Foundation that enrollment has been suspended for both SPID 0395 and SPID 0396. This decision has been made as a result of data received from the pivotal trials.